An image sensor is a semiconductor device that converts optical images into electrical signals.
The image sensor includes a photo detecting unit that detects light and a logic circuit unit that processes detected light into an electrical signal to make data.
In order to improve photo sensitivity of the image sensor, a fill factor, which is a ratio of the photo detecting unit to the whole area of the image sensor, must be increased. However, since the logic circuit part is an essential element in the image sensor, the expansion of the area of the photo detecting unit is limited by the logic circuit part.